Electrical pressure gauge



1,638,814 Aug. V9, 1927. H. EPSTEIN ELECTRICAL PRESSURE GAUGE Filed July 3. 1922 Il l. ||l

' 50 sistance Parental Aug. 9, i9z7-.-

PATENT OFFICE.

HIBBCE EPSTEIN, l' CHICAGO, ILLINOIS, METER C0., 0F CHICAGO, ILLINOI,

AssieNon 'ro Enano-'momie iinow' A CORPORATION OF'DELAWARE.

mera-roar. ranssuaii eenen.

Lipman med my a, im. serial im. annee.

My invention relates to pressure gauges in which mercury forms electrical connec-v tion with a series of resistances and theobjects of my improvements are, first, to accurately obtain the desired pressure at all times as the pressure changes; second, to provide a gaugeby means'of which anyi desired condition of combinations of factors may be obtained; third, to enable the insertion 'orf l0 connection of resistances varied by and measuring the pressure under different con ditions; fourth, to enable the insertion of resistances for correction purposes;.fifth` to so 4construct the device that leakage will be' prevented; sixth, to make a simple', practical and durable device, and other features tobecome ap arent from the description to follow: y invention comprisesa pressure chamber, an air chamber and a suitable ytube or pipe connecting'the two. -The connections l etween the tube or pipe and the pressure and air chamber are screw-threaded and sealed so that' there is no possibility of leakage., The tube or pipe is provided with. a series of electrical contacts arrangedl at diierent points along its length, preferably at graduated distances apart, which contactsI are connected with suitable resistances A quantity of mercury withinsaid tube or pipe is confined between the pressure in the pressure chamber and the 'pressure in the air chamber and its-position within said tube is varied by the varying pressure so that the pressure determines 'what amount-of resistance is connected in the circuit. The resistances of the series connected tothe plurality of contactsare predetermined with respect to the pressure, preferably according to a definite gradua- 40 tion, so that by ascertaining the quantity of resistance in the circuit the. pressure is attained. The resistance is measured by pleeing a balancing resistance in a Wheatstone bridge, in one leg of which are connected the w resistancesof the pressure gauge. The pressurewithin the gauge is at times varied by the wai-ying temperature of the air in the air chamber, or by other phenomena, .and to Yprovide a correctionfor this a suitable relocated in the air chamber isfcon nected in the circuit of the proper leg f the Wheatstone bridge. -v

- material.

vthe rise and fall of said To describe' my invention so'tbat others versed in the art to which it rtains can make and use the same, I have illustrated it on the accompanying sheet of drawing'forming a part of this'specification and in which: Figure 1, is a vertical central sectional view of a pressure gauge embodying my invention 1n its dpreferred form, diagrammatically connecte in fone leg of a Wheatstone bridge, and Figure 2, is a similar view showing a modification diagrammatically connected in one leg of a logarithmic Wheatstone bridge.

Similar reference cha'ractersrefer to similar parts throu hout'both views.

Referring to igure 1,-wi1'shjn the outer metal shell, or container, 3, is secured a tube or wel1,4, surmounted by a smaller tube, 5,

made of an desirable electrical insulating o the upper end ofthe tube, 5, is

secured a cap, 6, made in the form of an air lchamber. The lower end of the tube or well,

4, is open and terminates a short; distance above the bottom, 7, of container, 3, forinin an annular spacebetween the tube, 4, an

lower end of the container, 3. Piercing the tube, 5, and extending from its exterior to its interior are a plur'alit of .ontact pins, 8, arranged in a graduate manner from the bottom' to the top of the tube, 5. Suitable resistancesare connected between the' contacts, 8, in series, so that as diiie`rent'-con-A tacts are electrically connected and diecoirl nectedto the mercury 9, within tube 5, by mercury, the changes in thetotal resistance-can be measured in any suitable-manner.

A suitable quantity of'mercury, 9, is provided in the lower end of container, 3, and the tubes, 4, and 5, The iluidfspressure is admitted through a suitable p ipe connection, 10, to the interior 'of the container, 3, and of course is' exerted against the mercury, 9, in tubes, 4, and', and against `.the air in the air chamber, 6;. Obviosuly a greater'or less pressure withinrthe container, 3, will force themercury, 9, up into thetube, 5, 'a greater or-less distance, and the top'end of the tube, l

5, bein closed by the. air chamber, 6,. the air con ned in said chamber will therefore be-compressed to agreater or less degree as the mercury moves nlp and down in said tube, 5..- I prefer to fill t e vacant portion of the with an opening, 12, normally closed by a plug, for the purpose of placing the required amount of mercury, 9, and oil, 11, into the same. Another opening, 13, normally closed by a plug, is rovided in the bottom, 7, of

container, 3, or the purpose of removing the mercury, 9, and oil, 11, when it becomes necessary for repairs or other purposes. It will be noted that the same pressure exists within tube, 5, as in the container, 3, so that there is no tendency for any leakage from within the tube, 5, into the container, 3.

As'above mentioned, when the mercury, 9, rises in tube, 5, the amount ofresistance between the extreme contacts, 8, will be reduced and when the,mercury, 9, falls in tube, 5, theamount ofresistance between the extreme contacts, 8, will be increased, and to measure the amount of this resistance the extreme contacts, 8, are connected bysuit- .able conductors inf series in one arm of a Wheatstone'bridge, the said resistance being .designated as R2, the resistance connected in the companion arm being designated as Rr The resistanceRo is connected in one arm on the opposite side of the lvanometer and the balancing lresistance'R 1s connected in the companion arm thereto.

In the construction shown in Figure 1 above described, when the pressure gauge air temperature, i. e., the air in the air chamber 6, rises, the air will expand and depress the mercury in tube- 5,thereby increasing the resistance, R2, between the extreme con-4 tacts 8.

To make correction forthis .increased rel sistance, the resistance R4 in-the companion arm `is also increasedto the proper` extent, which will leave the balancing resistancR, which measures the pressure, unchanged by the temperature increase. Thisf is done by using for R4 a'resistance which rises with temperature. Y

To find the relation between the applied pressure, P, and the resultant preure inthe air chamber, P1, and the air temperature,

Tp, we note that an increase in the air chamber pressure, P1, can only result from a proportlonal increase in the applied pressure, P; and if for any given case weA also increase the air chamber temperature, Tp, it is evident that the increased pressure in the air chamber-will have to be balanced vby an` increase in the applied' ressure, I?, in order that the. mercury leve `in the air chamber should'remain where it was before the temperature was increased; in other words, the applied-pressure, P, must increase directly in proportion to the air chamber pressure,

P1, and the air' chamber absoluteA temperature, Tp. Therefor`e,'we may write:

Para, (Eq. #1.)

The relationshipbetween the resistances of Figure 1, and the elements they measure m: im

PK' :if-)1, since Por PIT .1 n (.See Eq. #1) where R,' R. R2, and R4,=r0-

slstances K0, K, K2, K,= constants or proportionality.

P=absolute pressure of gas in pounds per square foot.

' PL=eiective pressure in the air chamber.

Tp=pressure auge temperature.

In Figure 2, have illustrated a modified -form of my invention in which the pressure container 14 and the air container 15 are connected by a U shaped tube 16 made of any desirable-electrical insulating material which has the plurality of contacts 17 piercing it. on the leg below the container 14. The contacts 17 are exposedto the interior 'of the tube 16, are arranged in a graduated manner on differentlevels and are connected by suitable resistances as described in connection with FigureY 1. hecontainer 14 is preferably Iil1ed`with electrical insulating oil 11, and a suitable quantity of mercury, 9, is placed in the tube, 16. y

4 It will be noted that in the construction shown in Figure as the pressure increases,

additional resistances are cuil out of the cirl .cuit .while in the construction shown in Figure 2,- as the pressure increases additional resistances are connected into the circult. In each case, however, there 1s a relativelydefinite variance ofresistance for a given change of pressure, and by measuring the eifectiveresistance the desired pressurefis ascertained.

As above referred to, when thevf mercury 9 falls in the leg of tube 16,under the cha' ber v11i,`due to increasedl pressure`in said chamber, the amount of resistance between .the extreme contacts 17o, will be increased and when the mercury 9, rises, due to less pressure, the amount of resistance between .the extreme contacts, y17, will be decreased,

and -to measure the amount of this resistance, the extreme contacts, 17, are connected by suitable conductors in series in one arm of 'a logarithmic Wheatstone bridge, such as is disclosed in thepatent to Julius M.

Neiman for'l Logarithinie resistance circuit for measuring combinationsof different factors, issued zFebruary 23, 1926, Patent No.

(1,573,850, `the -sid resistance being designated as R2, the resistance connectedI in the companion arin being designated as R0. A

' resistance Ro is connected in. one arm on the opposite side of thegalvanometer and the balancing resistance R is connectedl in the companion arm thereto.

In the construction shown in Figure 2,

last above described, when the .pressure -guage air temperature, i. e., the air in the air yzo chamber 15, rises, the air will expand and depress the mercury iii-the leg of tub 16 `under chamber 15 which Will-cause the mer- Y ance It, is connected in the arm with the balancing resistance R to increasel the total resistance in said arm to the proper extent which will. leave vthe balancing resistance'R, which measures the pressure, unchanged by the temperature increase. This is done by. using for RL a resistance which rises with temperature. f

I have also illustrated in Figure .2 how pressure in combination with other factors canbe ascertained, giving for example the combination of factors necessary for measuring flow of gas.' which requires `that the` resistances R1 and R3 be connected in the.

same arm with theresistance R2.

-To measure the flow of gas it is necessaryv to ascertain the rvalues 'ofi-three variables, towit, the rate of flow of the gas past agiven point, the pressure ofthe gas thusl owing, and the specific gravityof the gas, with respect to air. Hence, lin order to` measure such flow, I make the resistances R1.. R2 and Itq proportional 'respectively to .said variables. i

The relationships'between the elements in! volved in 'Figure2 are: n

R2`=Ko log C21" s R1 =Kl0gal01rd R3=.K=1og,

v.01; 0 C., C, are constants of proportion aht l Isls-resistance calibration constant.

P=abso1ute pressure' of gas in pounds per square foot.

pd=pressure difference, pounds per square foot.

S-rspecitic gravity oi gas with` reference to air. e`

T=abso1ute temperature of gas cF'.

The balancing'resistance R may be automatically changed and/th'e change may indicated by a pointer?` measuring the balancing resistance, by means of a alvanoineter relay similar to that shown in the patent to ObermaienNo: 1,376,633 of May 3,1921.

it will be understan that einem, fm-m, and j arrangement ofi the parts may be, varied without in the least departing fromv the scope of my invention. .Y

Having thus fully d cribed my invention, what I claim as newand desire to secure by Letters Patent of the)U-nited States is:

1'. In a pressure measuring device, the4 combination of a closed gas chamber having a gas-.trapped therein, a pressure chamber envelopin-g said gas chamber and connected therewith, "means for imposingthe pressure to be measured upon the gas trapped in said gas'chambe'r, and" meansincluding a first resistance responsive'to the volume of the trapped gas; anda second resistance disposed in the enveloping pressure chamber .an varying withk theA temperature of the trapped gas and electrically connected with said first .resistance -for electrically determind ino ing the kpressurejto be measured as a combined mathematical function of thetemperature and volume of the trapped gas.

ing pressures, o gas chamber jrhaving a gas trapped therein, a pressure` lchaii'iber enveloping said as .chamberand'connected therewith, means or imposing thepressure to 'be 4measured upon the gas trapped g in said gas v chamber, a

Wheatstone bridge containing a pair. of roportionality resistaiicels.y ln one pairl o lts arms, an adjustable balancing resistance .in'one of the other arms, a Iresistance var ing as a function of?. the volume 'of t e trapped gas in the other arm, a resistance varying inversely with respect tosaid last resistance and as a function of the temperature of the trapped gas disposed in the envelopingcpressure chamber and connected in series -with the adjustable balanci-'iigjresistance iaid in the )balancing lresistance arm, said last. resistancebeing balanced against the resistance which varies as .a function o f. the volume ofthe trapped gas, and a.' cross connection. for the bridge, said balancing resistance measuringpressures imposed 2. I n a precisioninstrument for` measurj the combination of a closed upon the trapped gas as combined mathematical functions of` thetempelature and volume of the' trapped gas.

3. In a precision instrument for measuring pressures, the combination of a closed gas chamber having a gas trapped therein, a pressure chamber enveloping said gas chamber and connected therewith, means for imposing the pressure 'to be measured;- upon Qthe gas' trapped in said gas chamber, a

Wheatstonerbridge containing a pair of roportionality resistances in one pair o its arms, an adjustable balancing resistance in one of the other arms, a resistance varying as a function of the volume of the trapped gas intheother arma resistance varying inversely with respect to said last resistance and as a function of the temperature of the trapped gas connected in series with the ad'ustable balancing resistance and in the ba ancing resistance arm., 'said last resistance being balanced a inst the resistance which varles as a function of the volume of the tra pcd gas, and a cross connection for the bri ge, said balancing resistance measuring pressures imposed upon the trapped gas I as combined mathematicaly functions of the temperature and volume of the trapped gas. In testimony-whereof I have si ed my name to this specification this 17t day of June, 1922 at Chicago, Illinois.

` HIRSCH EPSTEIN. 

